This application relates to an improvement in a damper blade control as set forth in U.S. Ser. No. 09/111,826, filed Jul. 8, 1998, the disclosure of which is herein incorporated by reference.
In the above-specified application, a device for controlling the movement of the damper mounted in a housing between an open position and a closed position comprises a shaft rotatably secured to the damper for pivoting the damper between the open position and the closed position. A lever arm is mounted on the shaft for rotation therewith, and a spring is connected between the housing and the lever arm for normally urging the damper towards the open position. A motor and gear train is mounted on the housing and is actuable to overcome the force of the spring to move the damper to the closed position. A force translation arrangement in the form of a wind-up spool and a flexible band is disposed between the motor and the lever arm for translating the driving force of the motor when the motor is energized to move the damper to the closed position, and for gradually braking the motor due to its internal friction when the motor is de-energized and the spring returns the damper to the open position.
In particular, each device typically controls one or more damper blades mounted on respective shafts in a single housing. With the heating and cooling system in operation, the motor responds to a control arrangement which sends a signal corresponding to the thermostat in a specific zone of the system. The damper blade assembly is designed so that upon movement of the damper blades to their open position, slack will be created in the band thereby preventing damaging force from being transferred to the motor and its gear train. When the motor is energized as dictated by the control arrangement, the motor and gear train will rotate the spool such that the band will be wound thereon, and will transfer a pulling force which overcomes the spring to rotate the lever arm, the shafts and damper blades to their closed position at which a stop surface engages a stop post. It should also be seen that a portion of the spring is wrapped around a hub of the lever arm as the damper blades move to a closed position. As long as the motor continues to be energized, damper blades remain closed.
When the motor is de-energized, the force of the spring will reversibly rotate the lever arm, the shafts and damper blades, motor and gear train, which move together until the stop surface re-engages the stop post. In a damper designed without over-stress protection as provided by the above-mentioned application, the gear train and motor would be subjected to a sudden stop, inflicting almost certain damage to these drive elements. Because of the spool and flexible band which begins to unwind upon engagement between the stop surface and stop post, the motor and its gear train continue to rotate by their inertia and enable a gradual braking or slow down of motor and gear train due to internal friction to prevent damage thereto. The spool and flexible band thus act as a force translation arrangement in ensuring the positive opening and closing of damper blades without harm to the driving mechanism.
In using the damper control described above, it is noted that the only force counteracting the opening force of the spring is the internal friction of the motor and its gear train. Due to the fact that the blade opening is caused by a spring force and the blade closing is generated by a motor, the opening phase of the damper blades has a higher speed than the closing phase which results in problems of excessive noise, wear and overtravel of the motor and its gear train. In addition, unwinding of the band on the spool as the damper moves to its open position creates a time delay in rewinding the band on the spool when the motor is again energized to close the damper blades.
As a result, it is desirable to provide the damper blades with a control arrangement associated with the motor and its gear train for regulating the opening speed of the damper blades in a manner which will minimize the problems identified above. In one embodiment, it is desirable to provide an electrical control arrangement which will periodically energize the motor as the damper blades move from the closed position to the open position. In another embodiment, it is desirable to provide a mechanical control arrangement in which a dash pot is used to dampen the opening movement of the damper blade.